Pressure-sprayable water-soluble alkyl acrylate polymer solutions



United States Patent 3,305,511.1 PRESSURE-SPRAYABLE WATER-SOLUBLE ALKYLACRYLATE PGLYMER SGLUTHQNS Robert .l. Gander, Whitehouse, Ni, assignorto Johnson dz Johnson, a corporation of New .lersey No Drawing. FiledApr. 9, 1964, Ser. No. 358,642 19 Claims. (U. 26033.2)

The present invention relates to water-soluble filrnforming compositionsand more particularly to pressure sprayable solutions of water-solublefilm-forming polymers in which the propellent is the sole solvent forthe film-forming polymer.

Because of the convenience of application, it is becoming increasinglypopular to apply film-f0rming compositions from pressurized containersin the form of a fine mist or spray. The pressure is obtained byincluding in the container a highly volatile liquid that is a gas atordinary room temperatures and pressures. Because of the insolubility ofmost film formers in such volatile propellent liquids, it has been thepractice to first prepare a solution of the film-forming polymer in aconventional solvent, such for example as ethanol, ethyl acetate oracetone and then to charge the container with this solution and thepropellent liquids to be used.

These solvents, however, are generally not readily released by thefilm-forming polymer and tend to evaporate relatively slowly.Propellents, on the other hand, although present as liquids in thepressurized container are gases at normal room temperature and,accordingly, evaporate rapidly. I have discovered that polymers of alkylacrylates, both homopolymers and copolymers, with other monomers, aregenerally soluble in certain propel-lents, hereinafter called solventpropellents, where the alkyl group is not too small, i.e., where itcontains at least four carbon atoms and where the alkyl acrylate ispresent in amounts of at least 50% by weight of the polymer. However,all solutions of such acrylate polymers will not give satisfactorysp-rayable film-forming compositions. Also films formed from suchpolymers are insoluble in water and, accordingly, where applied to apatient, must either be peeled off or permitted to wear off, or mustotherwise be removed by the use of organic solvents.

It is an object of the present invention to prepare pressure-sprayablefilm-forming compositions wherein the sole solvent for the film-formingpolymer is the propellent and in which the film-forming polymer iswater-soluble. It is a further object to prepare pressure-sprayablesolutions of water-soluble alkyl acrylate polymers wherein the onlysolvent for the polymer is one of the propellent liquids used and whichwhen released from pressure through a dispensin valve in accordance withconventional aerosol technique will be dispensed in the form of a finespray or droplets. Qther objects and advantages of this invention willbecome apparent from the following description wherein are set foith byway of illustration and example certain embodiments of the same.

Although the alkyl acrylate polymers are found to be generally solublein propellent solvents where the alkyl group contains at least fourcarbon atoms and the alkyl acrylate is present in amounts of at least50% by weight of the polymer, these polymers are insoluble in watermaking it necessary to use organic solvents to remove the same afterapplication. it is, as previously indicated, for many uses highlydesirable to have such films water-removable so that the same, afterbeing formed, can be Patented Feb. 21, 1967 readily removed by washingwith water. These polymers can be made water-removable by including inthe acrylate polymer amine salts having the amine salt group designatedby the general formula where X is an acid anion of the group consistingof chloride, bromide and nitrate and the amine group is incorporatedinto the polymer through reaction with dimethylaminoethyl methacrylateor its salt. The active amine group which forms the salt, shouldgenerally be present in amounts of at least 1.0% by weight of the totalacrylate polymer in order to obtain water-removability of any acrylatepolymer film formed. Where the active group is present with the alkylacrylate in amounts of much less than 1.0% by weight of the acrylatepolymer, the desirable characteristic of water-removability will not bepresent after the salt is formed. The acid anion, however, appears to bea relatively active insolubilizing'agent insofar as efiectintg thesolubility of the acrylate polymer in propellent solvent is concerned.With increasing amounts above 1.8% by weight of in the acrylate polymer,the polymer salt becomes increasingly insoluble in the propellent.Accordingly, in practicing the present invention the amine group shouldbe present in amounts within the range of about 1.0% to 1.8%, based onthe weight of the polymer.

The solubi-lizing amine salts are incorporated into the polymer byusingpreferably, as one of the reactive monomers, dimethylaminoethylmethacrylate. The monomer use-d may be an amine salt. However, in thepreferred practice of the invention, the amine salts are not formeduntil after polymerization has been completed after which the acrylatepolymer containing the amine groups is converted to the amine salt byneutralization with an acid, the anion of which is to be added.

It is apparently the presence of the amine salt which causes thewater-solubilizing of the acrylate polymer to the point where films ofthe same can be removed from the skin by washing. It is also thepresence of the amine salt when present in too large amounts whichinhibits the dissolving of the polymer in the propellent solvent.Acrylate copolymers containing amine groups are found to be just asinsoluble in water as acrylate copolymers which do not contain the aminegroups. Also the presence of the amine group does not appear todeleteriously affect the solubility in propellent solvents. However,after the salts are formed by incorporating the acid ion into the aminegroup, the acrylate copolymers are solubilized to the extent that theycan be readily removed from the skin by washing with water. However,soluforming the salt is appreciably above 1.8%. This water solubilizingeffect, however, apparently only occurs where the solubilizing groupequivalent to 1.2% of group). However, if the concentration of thedimethylaminoethyl methacrylate hydrochloride is increased to 25.0% byweight of the polymer, the polymer is no longer sufficiently soluble inpropellent solvents, such for example as Freon 11, to completelydissolve in the same. (25.0% dimethylaminoethyl methacrylatehydrochloride is equivalent to 1.9% of the group.) This is wellillustrated by the following table:

other propellents are employed together with the solvent propellent togive the pressure desired.

Propellents As previously indicated, in practicing the present inventionthe film-forming polymer is not dissolved in the usual resin solventsbut is dissolved in a propellent solvent. The term propellent, as hereinused, is used in the conventional sense. A propellent is, for example,defined in Aerosols: Science and Technology, Interscience Publishers,Inc., New York, New York, page 214, as A liquefied gas with a vaporpressure greater than atmospheric pressure (14.7 p.s.i.a.) at atemperature of 105 F. This definition is sufficiently broad to includesome liquids which, used alone, would not function as propellents, butin solution with selected liquefied gases make satisfactory pressurizedsystems. An example is methylene chloride whose boiling point is 105 F.,at which temperature its vapor pressure equals .atmospheric pressure.Thus it just falls within the limits of thedefinition. At ordinary roomtemperature, methylene chloride has a vapor pressure below atmosphericpressure and cannot function as a propellent but, when dissolved in aliquid of high vapor pressure, it will give resultant pressuressatisfactory for application to an aerosol system.

Propellent solvents are those propellents which are also solvents forthe alkyl acrylate and alkyl methacrylate film-forming polymers used.

Propellent solvents generally available are trichlorofiuoromethane (CCIF), generally referred to in the trade as Propellent 11;dichlorofiuoromethane (CHCI F), generally referred to in the trade asPropellent 21; vinyl chloride (CH CHCI); and dimet hyl ether (CH OCHACRYLATE POLYMERS CONTAINING AMINE SALT GROUPS Polymer Composition,Weight Pereent N t Chloride Bromide Nitrate eu Rel. Vis. of Equiv. ofFree Base 2 Free Base 3 Water Fluoro- Water Fluoro- Water Fluoro- EHABACA DWAEMA Solubility carbon Solubility carbon Solubility carbonSolubility 5 Solubility Solubility 75 1.31 1,042 Insoluble Soluble;Insoluble Soluble Insolublc Soluble. 70 10 1.30 753 Soluble ...doSolublc. o Soluble Do. 65 10 1. 28 014 do Insoluble" do Insoluble doInsoluble.

1 EHA= 2-cthylhexyl acrylate; BACA N-tert.-butylacrylamide;DMAEMA=dimethylaminoetliyl methacrylate.

2 At a concentration of 1.000 g./100 ml. in toluene at 30 C.

3 By potentiometric titration in 50 benzene-ethanol using 0.1 Nethanolic hydrochloric acid.

4 At a concentration of 0.2 percent in'water.

5 At a concentration of 5 percent in 5&50 Propellents 11 and 12.

Although alkyl acrylate polymers and copolymers of the type hereindescribed are found to be soluble in propellent solvents, apressure-sprayable solution is not necessarily obtained. Sprayablecompositions or solutions are only obtained if the free base polymerused has a relative viscosity prior to conversion to its salt of notappreciably over 1.60 and is present in solution in the propellentsolvent in a concentration of not appreciably over 6.0% by Weight. As aviscosity of at least about 1.1 is needed in order to form a non-liquidfilm, the viscosity should preferably be within the range of about 1.20to 1.60. Free base polymer refers to the aminecont-aining polymer beforeconversion to the amine salt. Where the relative viscosity of thepolymer is appreciably greater than about 1.6, or where theconcentration in the propellent solvent is appreciably above 6.0%, a wetjet-like stream is obtained rather than a spray. Relative viscositiesare measured at 30 C. in toluene solutions of the polymer at aconcentration of 1.000 gram per 100 ml. The alkyl acrylate polymer filmsare applied by dispensing the same under pressure from a pressurizedcontainer wherein the polymer is present in the form of a solution inone of the propellents used. The propellent pressure in the container ispreferably in the range of about 20 to pounds per square inch gauge at atemperature of 75 F. Where the solvent propellent used will not byitself give a sufiiciently high total pressure,

Of these propellent solvents, the one preferred and the one found togive the best results with the Widest range of alkyl acrylate and alkylmethacrylate film-forming polymers is Propellent 11. Propellent 1-1 is agood solvent for the film-forming polymers and is readily released rbythe polymers after being dispensed from the (pressurized container.Where Propellent 11 is used as the propellent solvent, it is usedtogether with another propellent, such as Propellent 12,dichlorodifluoromethane, in order to increase the pressure in thecontainer to glge desired 20 to 60 pounds per square inch gauge at Withrespect to the other propellent solvents referred to, Propellent 21 is agood solvent for film-forming resins suitable for use in the presentinvention. This particular propellent solvent, however, has thecharacteristic that it is retained somewhat more tenaoiously by thealkyl acrylate and alkyl methacrylate polymers than is Rropellent 11even though it boils at a substantially lower temperature thanPropellent 11. This is apparently due to. the strong associativehydrogen bonding between Propellent 21 and the resin molecules.Accordingly, for the more rapid drying Propellent 11 is preferred.

The vinyl chloride propellent is a good solvent for the alkyl acrylateand alkyl methacrylate polymers. How ever, the vinyl chloride propellenthas the characteristic of being retained more tenaci'ously by thedissolved polymer, after the same has been sprayed into a film in'muchthe same manner as is Propellent 21. It, accordingly, gives a muchslower drying rate for the polymer film despite the fact that the vinylchloride boils at +7.9 F. As the vinyl chloride has a gauge pressure of34 pounds per square inch at 70 F., it can be used alone without afurther propellent. However, the flammable nature of the vinyl chloridetogether with its tendency to be retained by the alkyl acrylate andalkyl methacrylate polymers makes it generally unsuitable for use aloneas the propellent solvent in the preferred formulations of the presentinvention.

Dimethyl ether is another fairly good propellent solvent which is arelatively good solvent for the alkyl acrylate and alkyl methaorylatepolymers. The dimethyl ether has a boiling point of l2.7 F. and a gaugepressure at 70 F. of 60 pounds per square inch. However, the dimethylether is flammable and has an ethereal odor, both of which propertiesmake it generally unsuitable for surgical purposes when used aloneparticularly where sparks or open flame may be encountered.

As is clear from the above, the preferred propellent solvent isPropellent 11. The other propellent solvents can, however, be usedparticularly where used in blends with Propellent 11. They may also, insome instances, be used without any Propellent 11 being present.However, Propellent 11 is preferred, either as the sole propellentsolvent or as the major propellent solvent where blended with any of theother propellent solvents mentioned. The blending of Propellent 11 withvinyl chloride best illustrates some of the advantages obtained by usingat least some Propellent 11. Vinyl chloride has been indicated as beingflammable and, accordingly, generally undesirable in the preferredcompositions. However, the vinyl chloride can be used in minor amountsin blends with Propellent 11 and non-solvent Propellent 12 to givesatisfactory nonfiammable propellent compositions. For example, thefollowing formulations are nonflammable and give the indicated pressumeat 70 F.

Weight Percent Pressure at 70 F., p.s.i.g.

Prop. 11 Prop. 12 ViCl Propellent solution of film-forming polymer Aspreviously indicated, I have discovered that alkyl acrylate polymers aregenerally soluble in the propellent solvents, heretofore discussed,where the alkyl group contains at least four carbon atoms, the largerthe alkyl group apparently the more readily soluble the polymer. Thehomopolymers of the alkyl acrylates are readily soluble as are generallythe copolyrners of these monomers with other monomers particularly wherethe alkyl acrylate is present in the copolymer in amounts of at least 50percent by weight of the polymer.

The film to be formed may either be a permanently tacky film of thepressure-sensitive adhesive type or a dry protective film covering. Thisis controlled by the particular polymer or copolymer used. However,satisfactory propellent solutions of the polymer cannot be obtainedunless the free base polymer has a relative viscosity of not appreciablyover 1.60 and is present in the propellent solvent in a concentration ofnot appreciably over 6.0 weight percent.

Among the preferred polymers for practicing the present invention areterpolyrners of an alkyl acrylate, N-tertbutylacrylarnide, and ameth-acrylate containing an amine salt, such as dimethylaminoethylmethacryl'ate hydrochloride.

Either 2-ethylhexyl acrylate or n-butyl acrylate give excellentfilm-forming resins when polymerized with N- tert.-butylacrylamide andthe amine-containing methacrylate, subsequently converting the polymerto the amine salt. The lower alkyl acrylates, such as methyl or ethylacrylate, when used in these systems are generally unsatisfactory, asthe polymers obtained are not sufliciently soluble in the propellentsolvent.

The effect of concentration of polymer in the propellent solvent is wellillustrated by the following table. This table shows the spraycharacteristics of the hydrochloride salt of a terpolymer containing 70percent 2- ethylhexyl acrylate, 10 percent N-tert.-butylacrylamide and20 percent dimethylaminoethyl methacrylate. The terpolymer is dissolvedin a propellent solvent consisting of 50 percent trichlorofluoromethaneand 50 percent dichlorodifluoromethane. The ingredients are placed in6-ounce pressure cans which are closed with conventional aerosol spraynozzles.

Hydrochloride of ter- Spray character: polymer, wt. percent Fine spray3.0 Fine spray 5.0 Fine spray, but polymer precipitates and collects onthe valve orifice 7.0 Coarse wet spray with heavy precipitation ofpolymer on the valve orifice 9.0

The following examples given for the purpose of illustration only, willhelp to further illustrate the practice of the present invention.

EXAMPLE I A 5-liter, 3-neck flask is provided with a reflux condenser, amechanical stirrer, a nitrogen inlet tube, and a thermometer. The flaskis charged with 525 grams of 2-ethylhexyl acrylate, 150 grams ofdimethylaminoethyl methacrylate, grams of N-tert.-butylacrylamide and750 grams of ethyl acetate. The dimethylaminoethyl methacrylatc amountsto 20 percent of the monomer charge. During a 30-minute period thereaction mixture is heated to 7580 C. and stirred while a slow stream ofnitrogen is swept through the apparatus. The N-tert.- butylacrylamidedissolves during this heating period. Nitrogen flow is then discontinuedand 1.90 grams of 2,2- azobisisobutyronitrile are added. After aninduction period of a few minutes, an exothermic polymerization takesplace, causing the ethyl acetate to reflux vigorously. This soonsubsides, and the thickened reaction mixture is stirred and heated at 85C. for 3.5 hours. The reaction is then discontinued and the solutioncooled to room temperature. The solids content of a sample heated forfive hours at C. is 50.5 percent.

The ethyl acetate is dried from the polymer by casting the solution in athin film on silicone-coated paper, then drying at F. The polymer isvery tacky and has a relative viscosity of 1.31 (1.000 g./ 100 ml.toluene solution at 30 C.). The neutral equivalent of the polymer is780, measured by titrating samples potentiometrically with 0.1 Nethanolic hydrochloric acid in a solution of 50 percent benzene and 50percent ethanol.

The chloride salt of the polymer is prepared by new tralizing 100 gramsof the reaction mixture with 32.6 ml. of 1.99 N ethanolic hydrochloricacid. The chloride is dried on silicone-coated paper. It is a colorless,flexible, slightly tacky material which dissolves in water at l andslightly brittle.

a concentration of 0.2 gram per 100 ml. to give a turbid solution. Itdissolves at a concentration of percent in a blend of 50 percenttrichlorofiuoromethane and 50 percent dichlorodifiuoromethane, forming acolorless solution.

The bromide salt of the polymer is prepared by neutralizing 100 grams ofthe reaction mixture with 34 ml.

'of 1.91 N aqueous hydrobromic acid which is diluted with 34 ml. ofethanol. The film is colorless, non-tacky It is also soluble in waterand in a blend of 50 percent trichlorofiuoromethane and 50 percentdichlorodifluoromethane.

The nitrate salt of the polymer is prepared by neutralizing 100 grams ofthe reaction mixture with 34 ml. of 1.93 N aqueous nitric acid which isdiluted with 34 ml. of ethanol. The polymer is brown in color, flexibleand slightly tacky. It is also soluble in water and in a blend of 50percent trichlorofluoromethane and 50 percent dichlorodifiuoromethane.The above polymers are also soluble in all of the propellent solventsreferred to, pressurized solutions of about 3% solids giving excellentfilm-forming sprays.

EXAMPLE II No. Propellent Solvent 1 50% trichlorofiuoromethane50%dichloroditluoromethane. 90% vinyl chloride-% trichlorofluoromethane.

dichloroiluoromethane40% dichloroditluoromethane.

When discharged through the aerosol valve, each of the solutionsproduces a finely atomized spray of excellent appearance.

EXAMPLE III The polymerization procedure of Example I is repeated usinga monomer charge of 506 grams of Z-ethylhexyl acrylate, 169 grams ofdimethylaminoethyl methacrylate and 75 grams of N-tert.-butylacrylamide.The dimethylaminoethyl methacrylate amounts to 22.5 percent of themonomer charge. After polymerization, the reaction mixture has a solidscontent of 47.9 percent.

The polymer has a relative viscosity of 1.30 and a neutral equivalent of661.

Chloride, bromide and nitrate salts of the polymer are prepared as inExample I, using appropriate amounts of the various acids based on theneutral equivalent of 661.

Each of the three salts is soluble in water at a concentration of 0.2gram per 100 ml. The solubility behavior of the salts is as follows at 5percent concentration in three different fluorocarbon solvents:

Propellent solvent: Solubility 50% trichlorofiuoromethane50%dichlorodifluoromethane Partially soluble. 65 trichlorofluoromethane-35dichlorodifiuoromethane Soluble. 60% dichlorofiuoromethane-40%dichlorodifiuoromethane Soluble.

Particular embodiments of the invention have been used to illustrate thesame. The invention, however, is not limited to these specificembodiments. In view of the foregoing disclosure, variations ormodifications thereof will be apparent, and it is intended to includewithin the invention all such variations and modifications except as donot come within the scope of the appended claims.

Having thus described my invention, I claim:

1. In a pressurized system for spray application a solution of afilm-forming polymer in propellent the solvent for said polymer in saidsystem consisting essentially of propellent used in said system thepropellent of said system including at least one propellent solvent ofthe group consisting of trichlorofluoromethane, difluorochloromethane,vinyl chloride and dimethyl ether, said film-forming polymer being apolymer of an alkyl acrylate and dimethylaminoethyl methacrylate saidalkyl acrylate having an alkyl group of at least four carbons and beingpresent in said polymer in an amount of at least percent by weight, saidpolymer in the free base polymer form having an intrinsic viscosity ofnot over 1.6 and present in said solution in a concentration of not over6.0 percent by weight, said polymer containing about 1.0 to 1.8 percentby weight of the radical J where the radical is present in the salt formt I HX X being an acid anion of the group consisting of chloride,bromide and nitrate.

2. A pressurized system of claim 1 in which the acid anion of said groupis chloride.

3. A pressurized system of claim 1 in which the acid anion of said groupis bromide.

4. A pressurized system of claim 1 in which the acid anion of said groupis nitrate.

5. A pressurized system of claim 1 in which the major portion ofpropellent solvent is trichlorofiuoromethane.

6. In a pressurized system for spray application a solution of afilm-forming polymer in propellent the solvent for said polymer in saidsystem consisting essentially of propellent used in said system thepropellent of said systern including at least one propellent solvent ofthe group consisting of trichlorofiuoromethane, difiuorochloromethane,vinyl chloride and dimethyl ether, said film-forming polymer being apolymer of an alkyl acrylate polymerized with dimethylaminoethylmethacrylate, said alkyl acrylate being at least one of the groupconsisting of Z-ethyl-hexyl acrylate and n-butyl acrylate and beingpresent in said polymer in an amount of at least 50 percent by weight,said polymer in the free base polymer form having an intrinsic viscosityof not over 1.6 and present in said solution in a concentration of notover 6.0 percent by weight, said polymer containing about 1.0 to 1.8percent by weight of the radical Where the radical is present in thesalt form X being an acid anion of the group consisting of chloride,bromide and nitrate.

7. A pressurized system of claim 6 in which the acid anion of said groupis chloride.

8. In a pressurized system for spray application a solution of afilm-forming polymer in propellent the solvent for polymer in saidsystem consisting essentially of propellent used in said system thepropellent of said system including at least one propellent solvent ofthe group consisting of trichlorofluoromethane, difluorochloromethane,vinyl chloride and dimethyl ether, said film-forming polymer being aterpolymer of an alkyl acrylate, N-tert.-butylacrylamide anddimethylaminoethyl methacrylate said alkyl acrylate having an alkylgroup of at least four carbons and being present in said polymer in anamount of at least 50 percent by weight, said polymer in the free basepolymer form having an intrinsic viscosity of not over 1.6 and presentin said solution in a concentration of not over 6.0 percent by weight,said polymer containing about 1.0 to 1.8 percent by Weight of theradical where the radical is present in the salt form I 1IIHX X being anacid anion of the group consisting of chloride, bromide and nitrate.

9. A pressurized system of claim 8 in which said alkyl acrylate is atleast one of the group consisting of 2-ethylhexyl acrylate and n-butylacrylate.

10. A pressurized system of claim 9 in which the acid anion of saidgroup is chloride.

11. A pressurized system of claim 9 in which the acid anion of saidgroup is bromide.

12. A pressurized system of claim 9 in which the acid anion of saidgroup is nitrate.

13. In a pressurized system for spray application a solution of afilm-forming polymer in propellent, said propellent consistingessentially of 75 to 25 parts by weight of trichlorofluoromethane and 25to 75 parts by weight of dichlorodifluoromethane, said film-formingpolymer being a terpolymer of an alkyl acrylate, N-tert.-butylacrylamideand dimethylaminoethyl methacrylate, said alkyl acrylate having an alkylgroup of at least four carbons and being present in said polymer in anamount of at least 50 percent by weight, said polymer in the free basepolymer form having an intrinsic viscosity of not over 1.6 and presentin said solution in a concentration of not over 6.0 percent by weight,said polymer containing about 1.0 to 1.8 percent by weight of theradical where the radical is present in the salt form -I%IHX X being anacid anion of the group consisting of chloride, bromide and nitrate saidsolution containing no solvent for said film-forming polymer other thansaid propellents.

14. A pressurized system of claim 13 in which said alkyl acrylate is atleast one of the group consisting of 2- ethylhexyl acrylate and n-butylacrylate.

15. A pressurized system of claim 14 acid anion of said group isbromide.

16. A pressurized system of claim acid anion of said group is nitrate.

17. A pressurized system of claim acid anion of said group is chloride.

18. A pressurized system of claim alkyl acrylate is 2-ethylhexylacrylate.

in which the 14 in which the 14 in which the 17 in which the 19. Apressurized system of claim 17 in which the alkyl acrylate is n-butylacrylate.

References Cited by the Examiner UNITED STATES PATENTS 2,617,780 11/1952Lutz 26033.8 2,897,172 7/1959 Maeder 260-33.8 3,062,751 11/1962 Wahlin16782 MORRIS LIEBMAN, Primary Examiner. L. T. JACOBS, AssistantExaminer.

1. IN A PRESSURIZED SYSTEM FOR SPRAY APPLICATION A SOLUTION OF AFILM-FORMING POLYMER IN PROPELLENT THE SOLVENT FOR SAID POLYMER IN SAIDSYSTEM CONSISTING ESSENTIALLY OF PROPELLENT USED IN SAID SYSTEM THEPROPELLENT OF SAID SYSTEM INCLUDING AT LEAST ONE PROPELLENT SOLVENT OFTHE GROUP CONSISTING OF TRICHLOROFLUOROMETHANE, DIFLUOROCHLOROMETHANE,VINYL CHLORIDE AND DIMETHYL ETHER, SAID FILM-FORMING POLYMER BEING APOLYMER OF AN ALKYL ACRYLATE AND DIMETHYLAMINOETHYL METHACRYLATE SAIDALKYL ACRYLATE HAVING AN ALKYL GROUP OF AT LEAST FOUR CARBONS AND BEINGPRESENT IN SAID POLYMER IN AN AMOUNT OF AT LEAST 50 PERCENT BY WEIGHT,SAID POLYMER IN THE FREE BASE POLYMER FORM HAVING AN INTRINSIC VISCOSITYOF NOT OVER 1.6 AND PRESENT IN SAID SOLUTION IN A CONCENTRATION OF NOTOVER 6.0 PERCENT BY WEIGHT, SAID POLYMER CONTAINING ABOUT 1.0 TO 1.8PERCENT BY WEIGHT OF THE RADICAL